Ess does have a pluralistic grasp of grammar, and would be absolutely appalled if ever in Texas.
As for the litany of questions, there is a marked perception that pain is the only thing which makes people people. Pain is a part of many aspects which constitute the jangled web of mobile consciousness shuffling through this mortal coil declaring 'Ego sum solum unum!' to the Universe at large and otherwise. Which could care less. As Stephanos pointed out, Faith plays a major role irrespective of personal ideology. But the main thing which makes us human is physiology: we all basically look alike. Well, most of us. 2 arms, 2 legs, head above the shoulders, and compared to other bipeds, essentially hairless houseapes. To say pain is the only thing which unites all people only serves to cheapen what it is to be human.
There are a few other things which tie us all together, such as our noses. I've yet to meet someone where if another states 'Smell this, it's awful!' will not only smell that nasty scent, but take another whiff. No matter how refined we might think of ourselves, our noses are always that kid who pokes a stick at that dead thing in the ditch.
Another is racial memory, though it's been disputed. There resides in all that primal button marked 'FEAR' when we hear the wolves howl, or catch 'strange' noises while camping. There's something about night in unfamiliar territory that sets our hearts pumping. And there's always that neolithic rage which raises a stout tree limb on high screaming in a gutteral voice 'KILL THEM ALL!'. Most know how to suppress this, while there's some who just don't care. However, I've yet to hear of any who willingly and knowingly allowed loved ones to be injured or killed without the claws and fangs showing.
From whence do dreams come and why? There's a mountain of rather dry tomes on the subject. Except Freud. Now there's a one with some serious issues and not enough female contact. To answer that question, the answer is Yes, All The Above. There are times when our brains run screensavers while the rest of the neurons file the day's paperwork. Sometimes dreams serve the purpose of problem-solving. There was one time I was stuck while writing a mobprog for a MUD and the rather eloquent and simple solution to a complex problem came to me in a dream. And it worked perfectly. At other times dreams might be seen as portents as we subconsciously attempt to work through problems and fears, though there are times when we see far more than we give ourselves credit. And then there's just the strange stuff.
For example, I've written many pieces based on dreams I've had, where I was either the primary character, a physical observer, or at times a disembodied observer. Think of an articulated free-motion camera. Some have featured me while other dreams employ actors I've never met nor seen. The real oddity is being the primary actor and realizing that I'm not in my own body, that this is someone else, feeling like I'm in the backseat of a another's car. Try puzzling that one out.
As for truly understanding another, that is physically impossible. We can empathize, we can sympathize, but we can only be ourselves. Even identical twins don't really know what it's like to be the doppleganger. Any claim otherwise is pure delusion. You can only be yourself, though there's always those who put that to the test. Poor sods.
When one starts asking questions such as 'Why am I here?', 'What's it all mean when you get right down to it?', and 'Why do we think we think?', that only means one thing: too much freetime. The only answer I have is 42. Not just because Douglas Adams says so, but also because it's as good an answer as you're going to get.